Recently, in order to reduce air pollution caused by exhaust gases of vehicles, the vehicles are being manufactured based on studies for securing driving power by using an internal combustion engine and/or an electric motor. In this regard, the vehicles have been evolved in an order of a hybrid vehicle, a plug-in hybrid vehicle, and an electric vehicle. In this case, the hybrid vehicle and the plug-in hybrid vehicle include an internal combustion engine, an electric motor, and a battery pack, and the electric vehicle includes an electric motor and a battery pack without an internal combustion engine.
The battery pack includes at least one battery module. The battery module includes cartridges and battery cells. The cartridges are sequentially stacked on each other. The cartridges are tightly combined to each other by using a fastening unit, such as a bolt or the like. Also, the battery cell is located between the two facing cartridges. The battery cell includes a body portion and a pair of electrode leads. The body portion is mounted between the two cartridges, and includes a pouch packing material, and an electrode assembly and electrolyte sealed inside of the pouch packing material.
The electrode leads extends from the inside towards the outside of the body portion, and is formed of a metal plate having a plate shape. Here, the electrode lead protrudes outside of the cartridges through a gap between the cartridges or through a penetration split provided on a contact wall surface of the cartridges. The electrode lead is electrically connected to a neighboring electrode lead in series or in parallel, in consideration of capacity of the battery module or specification of an output voltage in the cartridges. Meanwhile, the number of battery cells of the battery module may increase in order to increase the capacity of the battery module or the size of the output voltage.
At this time, since the battery cells are mounted in the cartridges, when a stacked height of the cartridges increases, the size of the battery module may gradually increase together with the number of cartridges. Accordingly, when the battery pack is restricted from artificially expanding an accommodation space of the battery module, the increase of capacity of battery module or size of output voltage is limited by a structure of the battery pack. Also, the battery pack includes two or more battery modules to have large capacity. The battery modules are arranged in a horizontal direction and/or a vertical direction in the battery pack, and are electrically connected to each other in series or in parallel through a connection component, such as a bus bar, a connector, or the like.
However, the connection component occupies a certain space inside the battery pack because the connection component has any one of various shapes based on a design purpose of the battery pack. Here, when two or more battery modules are accommodated in the battery pack, the number of connection components increases together with the number of battery modules in the battery pack, and the battery pack has small energy density per unit volume according to the used number of connection components.